This invention relates to cartridge filters having a novel exit structure for reducing the pressure drop across the filter and to an improved method for filtering air or other fluids utilizing a cartridge filter.
This invention is especially useful in connection with an air filter and the like such as illustrated in U.S. Pat. No. 4,955,996 having an air filter cartridge utilizing pleated paper having a cylindrical configuration as a filter medium. Such filters have proved to be exceedingly effective in removing dust and the like and in filtering out chromate primer dust such as is removed in the mechanical stripping of commercial and military aircraft. Such filters having circular cross section are supplied by several suppliers including Dustex Corporation of Charlotte, N.C. Problems with utilizing such filter cartridges where air enters through the sides of the filter which are preferably elongated or at least arranged to present a large filter surface area involves relatively high pressure drops across the filter. The side entrance of fluid is important in such devices because of their greater capacity over those having an entrance end covered with filter material. It has been found that by utilizing apparatus and method in accordance with the present invention, a pressure drop may be reduced substantially as much as from one-fifth to one-tenth of the total former pressure drop. It has been found that the open end or orifice plate of such filter cartridges, having a circular exit opening represents approximately 90% of the pressure drop of the total assembled filter so enhanced flow through the end plate gives the most potential for improvement and pressure drop reduction.
Cartridge filters are utilized invariably with a wall or other barrier to separate the positive pressure area from the negative pressure area adjacent the open end plate.
It is contemplated that bellmouth elements such as are often utilized at the entrance end of fan housings or other air handling devices and ducts are utilized according to the present invention for collecting air delivered through side filter media for passing same to the opening in the orifice plate. Such a device may be used alone in combination or with an evase. An evase may also be used alone in the combination with the cartridge filter at the exit end. An evase of the type contemplated herein is often used at the exit end of fan housings and the housings of other components or ducts for the purpose of reducing the pressure drop at the exit end.